TABLE 3.1 NASA’s Demand for 238Pu, 2009-2028 (as of April 2008)

238Pu (kg)

Mission

Launch Date

Watts

Type of Radioisotope Power System

3.5

Mars Science Laboratory

2009a

100

MMRTG

1.8

Discovery 12/Scout

2014

250

ASRG

24.6

Outer Planets Flagship 1

2017

600-850

MMRTG

3.5

Discovery 14

2020

500

ASRG

5.3

New Frontiers 4

2021

800

ASRG

14

Pressurized Rover 1

2022

2000

High-performance SRGb

14

ATHLETE Rover

2024

2000

High-performance SRG

1.8-5.3

New Frontiers 5

2026

250-800

ASRG

3.5

Discovery 16

2026

500

ASRG

14

Pressurized Rover 2

2026

2000

High-performance SRG

5.3-6.2

Outer Planets Flagship 2

2027

700-850

ASRG

14

Pressurized Rover 3

2028

2000

High-performance SRG

105-110

Total demand for 238Pu, 2009-2028 (kg)

 

 

 

5.3-5.5

Annual demand (20-year average in kg/year)

 

 

 

NOTE: ASRG, Advanced Stirling Radioisotope Generator; ATHLETE, All-Terrain Hex-Legged Extra-Terrestrial Explorer; MMRTG, Multi-Mission Radioisotope Thermoelectric Generator; SRG, Stirling radioisotope generator.

aThe launch date for the Mars Science Laboratory mission is currently 2011.

bA high-performance SRG is a yet-to-be-developed concept that would use ASRG technology to meet the high power requirements of the lunar rovers.

SOURCE: Letter from the NASA administrator Michael D. Griffin to secretary of energy Samuel D. Bodman, April 29, 2008 (reprinted in Appendix C).

demand for 238Pu.3 The committee has chosen to use this letter as a conservative reference point for determining the future need for RPSs (see Table 3.1). However, the findings and recommendations in the report are not contingent upon any particular set of mission needs or launch dates. Rather, they are based on a conservative estimate of future needs. The estimate of future needs is also consistent with historic precedent. For example, the mission set described in the administrator’s letter is consistent with the mission set in the current Agency Mission Planning Model, although the latter includes three additional RPS-powered missions: two International Lunar Network missions (that could be launched in 2013 and 2016) and a Mars Lander mission (that could be launched in 2016). These additional missions are not included in Table 3.1, but the total amount of 238Pu required to fuel these additional missions is estimated to be 3.6 kg or less. As noted below, even if the 238Pu required by these missions is not considered, the DOE should take immediate action to reestablish domestic production of 238Pu. Including the International Lunar Network and Mars Lander missions in the demand estimate would only increase the projected 238Pu shortfall.

The administrator’s letter requests that the DOE maintain the capability to provide NASA with fueled RPS assemblies for 12 missions during the 20-year period from 2009 to 2028. These missions have electrical power requirements ranging from 100 to 2,000 watts (see Table 3.1).

The amount of 238Pu required to meet the needs of these 12 missions will depend upon the type of RPS used to convert the thermal energy of the 238Pu fuel to electrical energy. The Mars Science Laboratory is equipped with a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), and the MMRTG is also currently baselined for use on the Outer Planets Flagship (OPF) 1 mission. As Chapter 4 describes in more detail, this is the only type of RPS that is currently available, and it has a low energy-conversion efficiency (of just 6.3 percent). The Advanced Stirling Radioisotope Generator’s (ASRG’s) energy conversion efficiency is predicted to be 28 to 30 percent, and an ASRG will produce more electricity than an MMRTG even though it will be powered by just two general purpose heat source (GPHS) modules instead of the eight modules used by an MMRTG.

The ASRG or some other type of Stirling radioisotope generator is baselined for all other missions listed in the administrator’s letter.4 All 12 missions will require a total of 105 to 110 kg of 238Pu, which is equivalent to an average production rate of 5.3 to 5.5 kg per year for 20 years.

3

Letter from the NASA administrator Michael D. Griffin to secretary of energy Samuel D. Bodman, April 29, 2008 (reprinted in Appendix C). During the late 1980s and early 1990s, NASA periodically sent similar letters to DOE to update DOE regarding NASA’s requirements for 238Pu.

4

As described in Chapter 4, the International Lunar Network missions, if they take place, would likely be powered by a third type of RPS: a yet-to-be-defined “Small RPS.”



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